All-optical switches on a silicon chip realized using photonic crystal nanocavities

We demonstrate all-optical switching in the telecommunication band, in silicon photonic crystals at high speed (similar to 50 ps), with extremely low switching energy (a few 100 fJ), and high switching contrast (similar to 10 dB). The devices consist of ultrasmall high-quality factor nanocavities connected to input and output waveguides. Switching is induced by a nonlinear refractive-index change caused by the plasma effect of carriers generated by two-photon absorption in silicon. The high-quality factor and small mode volume led to an extraordinarily large reduction in switching energy. The estimated internal switching energy in the nanocavity is as small as a few tens of fJ, indicating that further reduction on the operating energy is possible. (C) 2005 American Institute of Physics.